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v3.25.2

Other Real Estate Owned (Tables) | 6 Months Ended
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Jun. 30, 2025
Other Real Estate Owned |
Schedule of activity in the other real estate owned (OREO) portfolio, net of valuation reserve | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Six Months Ended
​ |  | June 30, |  | June 30,
Other real estate owned |  | 2025 |  | 2024 |  | 2025 | ​ | 2024
Balance at beginning of period | ​ | $ | 2,878 | ​ | $ | 5,123 | ​ | $ | 21,617 | ​ | $ | 5,123
Property additions, net of participation sold | ​ | ​ | 4,989 | ​ | ​ | 3,388 | ​ | ​ | 4,989 | ​ | ​ | 3,388
Less: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Carrying value of property disposals, net of participation sold | ​ | ​ | 1,224 | ​ | ​ | 1,591 | ​ | ​ | 19,509 | ​ | ​ | 1,591
Period valuation adjustments | ​ | ​ | 157 | ​ | ​ | - | ​ | ​ | 611 | ​ | ​ | ​
Balance at end of period | ​ | $ | 6,486 | ​ | $ | 6,920 | ​ | $ | 6,486 | ​ | $ | 6,920
Schedule of activity in valuation allowance | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​ | Six Months Ended
​ |  | June 30, |  | June 30,
​ |  | 2025 |  | 2024 |  | 2025 |  | 2024
Balance at beginning of period | ​ | $ | 853 | ​ | $ | 118 | ​ | $ | 1,862 | ​ | $ | 118
Provision for valuation reserves | ​ | ​ | 157 | ​ | ​ | - | ​ | ​ | 611 | ​ | ​ | -
Reductions taken on sales | ​ | ​ | (448) | ​ | ​ | - | ​ | ​ | (1,911) | ​ | ​ | -
Balance at end of period | ​ | $ | 562 | ​ | $ | 118 | ​ | $ | 562 | ​ | $ | 118
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Schedule of expenses related to foreclosed assets, net of lease revenue | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Six Months Ended
​ | ​ | June 30, |  | June 30,
​ |  | 2025 |  | 2024 |  | 2025 | ​ | 2024
(Gain) Loss on sales, net | ​ | $ | (76) | ​ | $ | (259) | ​ | $ | 160 | ​ | $ | (259)
Provision for valuation reserves | ​ | ​ | 157 | ​ | ​ | - | ​ | ​ | 611 | ​ | ​ | -
Operating expenses | ​ | ​ | (393) | ​ | ​ | 239 | ​ | ​ | 1,520 | ​ | ​ | 352
Less: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Lease revenue | ​ | ​ | (347) | ​ | ​ | 67 | ​ | ​ | 383 | ​ | ​ | 134
Net OREO expense | ​ | $ | 35 | ​ | $ | (87) | ​ | $ | 1,908 | ​ | $ | (41)
​

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- Definition Tabular disclosure of expenses related to foreclosed assets, net of lease revenue. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings. + References No definition available. + Details
Name: | osbc_OtherRealEstateExpensesRelatedToForeclosedAssetsTableTextBlock
Namespace Prefix: | osbc_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

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- Definition Tabular disclosure of the change in valuation allowance of other real estate on properties acquired through foreclosure. + References No definition available. + Details
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Namespace Prefix: | osbc_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
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- Definition Tabular disclosure of the change in other real estate on properties acquired through foreclosure. + References No definition available. + Details
Name: | osbc_RealEstateAcquiredThroughForeclosureRollForwardTableTextBlock
Namespace Prefix: | osbc_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_RealEstateAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration